Electrostatic chucks are widely used to hold substrates, such as semiconductor wafers, during substrate processing in processing chambers used for various applications, such as physical vapor deposition (PVD), etching, or chemical vapor deposition. Electrostatic chucks typically include one or more electrodes embedded within a unitary chuck body, which comprises a dielectric or semi-conductive ceramic material across which an electrostatic clamping field can be generated. Semi-conductive ceramic materials, such as aluminum nitride, boron nitride, or aluminum oxide doped with a metal oxide, for example, may be used to enable Johnsen-Rahbek or non-Coulombic electrostatic clamping fields to be generated.
Variability of the chucking force applied across the surface of a substrate during processing can cause an undesired deformation of the substrate, and can cause the generation and deposition of particles on the interface between the substrate and the electrostatic chuck. These particles can interfere with operation of the chuck by affecting the amounts of chucking force. And when substrates are subsequently moved to and from the chuck, these deposited particles can also scratch or gouge the substrates and can ultimately lead to breakage of the substrate.
Non-uniform or excessive heat transfer between a substrate and the electrostatic chuck can also cause damage to the substrate and/or chuck. For example, an overchucked substrate may result in an excessively large area of contact or an excessively concentrated area of contact between the substrate and chuck surfaces. Heat transfer occurring at the area of contact may exceed physical limitations of the substrate and/or chuck, resulting in cracks or breakage, and possibly generating and depositing particles on the chuck surface that may cause further damage.
Electrostatic chucks are therefore sometimes coated with a patterned coating. In some cases, the coating is applied through a mask. Conventional masks used for coating electrostatic chucks are typically aluminum oxide, and are secured to a coating apparatus using screws or other fasteners that constrain movement of the mask. Under the extreme heat cycling encountered during typical coating operations, the masks crack and fail in a relatively short period of time. Thus, there is a need for better masks for coating electrostatic chucks.